What was lavoisiers actual oxygen theory of combustion?
Answer:
"We observe in the combustion of bodies generally four recurring phenomena which would appear to be invariable laws of nature; while these phenomena are implied in other memoirs which I have presented, I must recall them here in a few words."- Antoine Laurent Lavoisiers
First Phenomenon. In all combustions the matter of fire or light is evolved.
Second Phenomenon. Materials may not burn except in a very few kinds of air, or rather, combustion may take place in only a single variety of air: that which Mr. Priestley has named dephlogisticated air and which I name here pure air. Not only do those bodies which we call combustible not burn either in vacuum or in any other species of air, but on the contrary, they are extinguished just as rapidly as if they had been plunged into water or any other liquid.
Third Phenomenon. In all combustion, pure air in which the combustion takes place is destroyed or decomposed and the burning body increases in weight exactly in proportion to the quantity of air destroyed or decomposed.
Fourth Phenomenon. In all combustion the body of which is burned changes into acid by the addition of the substance which increases its weight. Thus, for example, if sulfur is burned under a bell, the product of the combustion is vitriolic acid; if phosphorus be burned, the product of the combustion is phosphoric acid; if a carbonaceous substance be burned, the product of the combustion is fixed air, formerly called the acid of chalk, etc.[2]
The oxygen theory of combustion resulted from a demanding and sustained campaign to construct an experimentally grounded chemical theory of combustion, respiration, and calcination. The theory that emerged was in many respects a mirror image of the phlogiston theory, but gaining evidence to support the new theory involved more than merely demonstrating the errors and inadequacies of the previous theory. From the early 1770s until 1785, when the last important pieces of the theory fell into place, Lavoisier and his collaborators performed a wide range of experiments designed to advance many points on their research frontier.
Lavoisier's research in the early 1770s focused upon weight gains and losses in calcination. It was known that when metals slowly changed into powders (calxes), as was observed in the rusting of iron, the calx actually weighed more than the original metal, whereas when the calx was “reduced” to a metal, a loss of weight occurred. The phlogiston theory did not account for these weight changes, for fire itself could not be isolated and weighed. Lavoisier hypothesized that it was probably the fixation and release of air, rather than fire, that caused the observed gains and losses in weight. This idea set the course of his research for the next decade.
.for more info, refer to http://web.lemoyne.edu/~giunta/lavoisier...
combustion requires O2 and is a result of oxidation of a substance by the oxidizing agent Oxygen through its removal of Hydrogen (electrons) resulting in the formation of H2O
maybe this site will help you...
http://en.wikipedia.org/wiki/antoine_lav...
Back around 1690-1710 Johannes Becher and his student Stahl put forward the idea that combustion was the release of an hypothetical substance called phlogiston from combustible materials into the air. By this they meant that fuels like oil, wood, coal and charcoal were rich in phlogiston. Air had a limited capacity for phlogiston (according to the idea) so when combustion was attempted in a limited volume as in a sealed container it soon stopped.
Smelting was the opposite, phlogiston transferred from fuels like charcoal to metal ores, which they though of as the simplest form, to make the metal, which was considered to be a compound of the ore and phlogiston.
The theory explained some things neatly but had the great disadvantage that the products of combustion weighed more than the fuel, and that the weight of metal obtained was always less than the ore. Therefore phlogiston must have had negative weight, which is an extraordinary property. It could also pass through the walls of containers in some circumstances, another extraordinary property. Since most containers leaked anyway, and people rarely weighed anything these extraordinary properties went without much notice.
The ideas came from old alchemical ones of "earth, air, fire & water" where the ores represented the earthy element, while phlogiston was the "fire" element.
In about 1750 the Scots chemist Joseph Black (who taught chemistry to James Watt of steam engine fame) discovered carbon dioxide, which was called "fixed air". This made the phlogiston theory look shaky because it did not quite fit in. However the theory was stretched to more or less cover it.
In 1773 a new gas was discovered by Carl Scheele in Sweden and several months later, quite independently by Joseph Priestley in England. (Priestley was a friend of Watt, also of Ben Franklin, Dr. Erasmus Darwin and the potter Josiah Wedgwood. Darwin and Wedgwood were Charles Darwin's grandfathers). This gas supported life in a closed container longer than ordinary air and made burning very fierce.
During the 1760s and 1770s French experimental chemists began to use sensitive balances to weigh the reactants and products of reactions, Lavoisier, who was a tax collector by day job led them. Lavoisier was used to keeping financial accounts, which might have had a bearing on what happened.
Priestley visited Lavoisier in Paris with news of the new gas, which he called "de-phlogistated air" or "eminently respirable air" because he found it supported combustion and life much better than ordinary air. By this time, or soon after they had made the remarkable discovery that the air we breathe was actually a mixture of about a fifth of Priestley's new "air", four fifths of a more or less inert gas and a trace of Black's "fixed air". Some time later Lavoisier heard of Scheele's discovery too when his book on the subject was finally published.
The big problem with the phlogiston theory was that it meant that phlogiston had extraordinary properties. It is a principle of science that the simpler explanation is usually correct and the assumption that something has really odd properties is usually wrong. See "Occams razor".
Lavoisier saw almost immediately that if the new air was so good in combustion and made up part of ordinary air, then combustion was more simply explained by presuming that it was a reaction of the new air with fuel. That explained the weight differences very well and eliminated the extraordinary substance phlogiston.
Over the next few years Lavoisier carried out many experiments with air, oxygen, metals and sealed containers and managed to show that the increase in weight of mercury burnt in a closed container was equal to the amount of air removed from the container. Thus his chemical books balanced just like his tax ones. This and many other experiments showed that the phlogiston theory was incorrect.
Lavoisier and other French chemists then went on to show that for instance sulphuric acid was formed by the reaction of the Scheele/Priestley air with sulphur, then dissolving the product in water. The same happened with carbon and other materials and they named the air "oxygene" meaning "acid giver".
Priestley never accepted that the phlogiston theory was incorrect. Lavoisier was executed during the "Reign of Terror" in the French Revolution because he or his father had bought an aristocratic title.
Antoine-Laurent de Lavoisier (August 26, 1743 – May 8, 1794) the "father of modern chemistry," was a French nobleman prominent in the histories of chemistry, finance, biology, and economics. He stated the first version of the law of conservation of mass, co-discovered, recognized and named oxygen (1778), as well as hydrogen, disproved the phlogiston theory, introduced the metric system, wrote the first extensive list of elements, and helped to reform chemical nomenclature. He was also an investor and administrator of the "Ferme Générale," a private tax collection company; chairman of the board of the Discount Bank (later the Banque de France); and a powerful member of a number of other aristocratic administrative councils. Because of his prominence in the pre-revolutionary government in France, he was beheaded at the height of the French Revolution.
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